Power supply units supplying a consumer with a low voltage by transforming the supply voltage into the required low voltage by means of a voltage transformer are nowadays widely spread. It is necessary for certain applications, e.g. for charging outdoor equipment, that the power supply unit can be safely operated in moist environment. Here, the protection class IPx4, or even IPx7 has to be observed.
As is generally known, the so-called IP code (Ingress Protection) relates to the protection against splashing water all-around (IPx4) and the protection against temporary submersion (IPx7) according to the Standard DIN EN 60529 [DIN EN 60529 (VDE 0470-1):2000-09 Protection Classes by casings (IP-Code) (IEC 60529:1989+A1:1999); German Version EN 60529:1991+A1:2000. VDE-Verlag, Berlin].